1. Field of the Invention
The present invention relates to a method of load reduction on a buried culvert using an EPS block, and more particularly, to a method of load reduction on buried culvert using an EPS block, in which the EPS block is placed in the form of a multi-layered structure or the EPS block and geosynthetics are placed to maximize an earth arching effect due to artificial compression and deformation of EPS blocks and earth pressure reduction due to progress of deformation and maximize an arching effect because of pull-out resistance of earth and geosynthetics occurring when the EPS blocks are compressed in case of geosynthetics, thereby preventing an increase of culvert section due to high fill and an increase of vertical load due to a relative settlement difference of surrounding earth, which occurs from buried culvert on the weak ground.
2. Background of the Related Art
In general, a culvert, which is a structure buried underground or road embankment, is a water flow channel, or which is covered not to show water surface on the surface of the earth. In case that the culvert is applied to engineering works, it forms a channel for rainwater, sewage and water for industrial and agricultural uses or is used to make a passage, such as a footway or a roadway. Also, it may be used in an underground common duct for burying electric communication and hot and cool culverts.
The culvert is divided into a rigid pipe, a semi-rigid or a soft according to rigidity of material. The rigid type culvert is used as a concrete pipe and a cast iron pipe. The soft type culvert is made of steel material, and the section of the pipe is in the form of a round, a rectangle, an egg, or an oval circle.
Meanwhile, the culvert constructed under the road serves to transmit high filling of a road embankment and vehicle load to the ground, and to allow small vehicles and people who want to cross a road to pass below the road. Therefore, the culvert requires characteristics capable of sufficiently supporting equally distributed loads by a banking load and a traffic load as an underground structure and preventing ground settlement.
Furthermore, the culvert is classified according to used materials, sectional shape and construction methods. The reason is that a load acting on the culvert is varied according to buried methods of the culvert.
The culvert is classified into a ditch condition, a projecting condition and a tunnel condition according to the construction methods.
The ditch condition means that a trench is formed in a burial depth and the culvert is buried, the projection condition means that the culvert is put on the original ground surface and filling earth is banked on lateral sides and the top surface of the culvert, and the tunnel state means that the ground is directly tunneled by tunneling methods of various kinds and the culvert is installed.
The most important load acting on the culvert is gravity.
A formula for calculating a load acting on the culvert is expressed only by the vertical element, and the horizontal element is determined according to the ratio of the load of the calculated vertical element.
The load acting on the culvert includes the following matters:
first, a load of a downward force vector acting on the upper plane of the culvert; and
second, a resultant force vector of a base reaction force acting on the lower plane of the culvert upwardly.
At this time, the upward base reaction force has the same value as a total load acting downwardly if a foundation of culvert to withstand the total upward force is sufficient.
The load acting on the culvert is largely classified into two: first, a load by surroundings of the culvert and filling material of the top surface; and second, a overburden pressure in which load generated from the outside is transmitted through the filling material.
At this time, the overburden pressure acts as a concentrated load if being equal to a truck-axial load, and acts as a distribution load if construction materials are piled up on the filling material.
A vertical load of the culvert is calculated as follows (guide book of embankment and culvert temporary structure construction (1986), issued by Japanese Road Associationxe2x80x94Korea applies the same standards):
P=xcex1xcex93H
wherein P is vertical load, xcex1 is a load coefficient, xcex93 is a unit weight of filling material, and H is overburden of the upper plane of culvert.
At this time, xcex1 has the following value:
1) if the foundation ground is good and a pile foundation is not used, xcex1 is 1.0.
2) if a box type culvert is constructed on the weak ground,
wherein B is a horizontal breadth of a culvert.
As described above, the load acting on the upper part of the culvert is larger than a self-weight of the upper filling material, xcex93H. The reason is that not only the self-weight of the upper filling material but also downward shear force between the interior prism and the exterior prism are added and act on the top surface of the culvert. Lots of search results carried out in the U.S show the above fact, and many regions in Japan and Korea adapts it as a standard.
Furthermore, damage of the culvert occurs when exact analysis and consideration of differential settlement between a direct upper part and a side part of the culvert, i.e., an additional load according to relative deformation, a stress concentration phenomena of connected parts, differential settlement of culvert foundation are not reflected in design, and construction methods and management of quality suitable for field conditions are not managed according to proper standards. So, effective supplementations to the above have been demanded.
An induced ditch culvert is manufactured to reduce the vertical load acting on the upper part of the culvert. The induced culvert is manufactured by performing the steps of constructing the culvert like a forward projecting culvert, excavating to a horizontal volume of the culvert and the top surface of the culvert after filling material is banked on the side and upper parts of the culvert, and banking again with very smooth and compressible material. At this time, straws, bales of hay or organic earth were filled as the filling material. However, their stress-strain behaviors is unpredictable and uncontrollable and it can result in a potential explosion hazard as a result of the methane gas generation that accompanies anaerobic decomposition of organic material in a confined space.
Therefore, instead of using the straws, haystacks or organic earth, which are compressible materials, a method for placing an EPS on the top surface of the buried culvert has been used to reduce the horizontal and vertical loads applied to the buried culvert.
The EPS (Expanded Polystyrene) block is called Styrofoam, and called foamed styrene in the industrial field. The EPS is made by performing the steps of adding foaming agent to polystyrene resin of a grain type, foaming gas at the same time with heating and softening.
The EPS block first applied as engineering material by the Norwegian Road Research Laboratory (NRRL) on 1972 has been verified as a lightweight fill material for geotechnical engineering for 30 years.
An EPS banking refers to a method applied to engineering and construction works, such as roads embankment, railways and land preparation, using a large-sized EPS block as banking material and filling material because the EPS block has super-lightness, compression resistance, water resistance, independence.
FIG. 1 is a schematic view of the structure of a construction section of a conventional buried culvert. As shown in the drawing, foundation excavation was performed at a place, where a culvert will be buried. Land grading was performed at the ground of the excavated place, and after that, mat and rubble stones were placed and the culvert 1 was put. After that, material was filled directly. Alternatively, an EPS block 2 was placed before the filling earth was banked, and the EPS block 2 was placed, and then, filling earth was banked and compacted to be equal to a required elevation.
Total stress Wxe2x80x2 acting on the top surface of the culvert 1 is calculated as follows:
if the EPS block 2 is not placed, Wxe2x80x2=W=P=xcex1xcex3H (wherein W is a self-weight of filling earth, xcex1 is 1.0xcx9c1.6, xcex3 is a unit weight of filling earth, and H is overburden of the upper plane of a culvert), and
if the EPS block 2 is placed, Wxe2x80x2=Wxe2x88x922F (wherein F is a friction force induced by compression of EPS block).
If the culvert 1 is buried in a state that the EPS block is not placed, it is highly possible that the culvert is damaged. Such damage of the culvert may cause stress concentration of culvert connecting parts and non-uniform settlement of culvert foundation. Even though the EPS block is placed to prevent the above problems, there is a problem that the greatest vertical earth pressure reduction is not obtained when a largely vertical load is acted.
Accordingly, the present invention is directed to a method of load reduction on buried culvert using EPS blocks that substantially obviates one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a method of load reduction on a buried culvert utilizing compressibility of an EPS block, which is used as a filler upon a road construction and an abutment construction, thereby preventing an increase in the section of the culvert due to banking and an increase in a vertical load due to a relative settlement difference of surrounding earth of the buried culvert on the weak ground.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, an EPS block is placed in the form of a multi-layered structure between filling earth while filling earth is banked on the top surface of a culvert, which is buried, wherein the upper EPS block is placed on a plane of equal settlement.
In another aspect of the present invention, the EPS block is placed on the top surface of the culvert, and geosynthetics is placed on the EPS block.
It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.